In addition to what Kevin said, perhaps you are looking for macros from this
file:
https://github.com/RcppCore/Rcpp/blob/master/inst/include/Rcpp/macros/dispatch.h
Le 14 févr. 2014 à 00:34, Søren Højsgaard <sor...@math.aau.dk> a écrit :
> Dear all,
>
> Function foo_num below takes a numeric vector and returns a list with the
> first element of the vector. (Not very interesting function). I want to
> create a templated version of this in function do_foo below, but whether "a"
> should be a double, an integer, or a string depends on the RTYPE.
>
> My question is (and it is embarrasing to ask because I believe Romain has
> already answered it; just can't find the answer) how to derive the what type
> "a" should have once we know RTYPE??
>
> My second question is: Isn't there an easier general way to write the
> dispatch function (I have in mind situations where the templated function
> takes *more* than one argument!)? I have in mind something like:
>
> int type = TYPEOF(XX_) ;
> return do_foo<type> ( XX_ ) ;
>
> but that fails because INTSXP, REALSXP etc seems to be defined as const's
> (thats my reading of the compiler message).
What goes into template parameters is compile time constant. And the type of an
R object is dynamic, there is no way to know before runtime, so the compiler
can not do this for you.
>
> Thanks
> Søren
>
>
> #include <Rcpp.h>
> using namespace Rcpp;
> //[[Rcpp::export]]
> List foo_num(NumericVector x){
> double a=x[0];
> return List::create( a );
> }
>
> template <int RTYPE>
> List do_foo( Vector<RTYPE> x ){
> double a=x[0]; // WHAT TO DO HERE???
> return List::create( a );
> }
>
> SEXP foo_any( SEXP& XX_){
> int type = TYPEOF(XX_) ;
> switch( type ){
> case INTSXP : return do_foo<INTSXP> ( XX_ ) ;
> case REALSXP : return do_foo<REALSXP>( XX_ ) ;
> case STRSXP : return do_foo<STRSXP> ( XX_ ) ;
> }
> return R_NilValue ;
> }
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